1. Field of the Invention
The present invention relates to hand lever apparatus for operating a driven member such as a throttle valve of an internal combustion engine through a cable and more particularly, to a hand lever apparatus arranged near a grip portion of a handle of a work machine such as a grass trimmer or a hedge trimmer and suited for operating the throttle valve through a throttle cable or the like.
2. Description of the Prior Art
Conventionally, in a work machine such as a grass trimmer or a hedge trimmer in which a working unit including of a cutter is generally driven by an internal combustion engine and which has the aim of adjusting the output of the driving internal combustion engine by hand, a hand lever apparatus for adjusting of the opening of a throttle valve of the internal combustion engine is arranged near a grip portion of a U-shaped handle or a bar handle provided for the work machine.
The hand lever apparatus has a throttle trigger (throttle lever) typically operated by fingers of an operator. By rotationally operating the throttle lever, the opening of the throttle valve can be adjusted through the throttle cable. The throttle valve is normally biased to a minimum opening (idle rotation opening) so that the idle rotation opening may be maintained under the intact condition in which the throttle lever is not operated. When the throttle lever is operated to pull the throttle cable by a predetermined length or more to cancel out a play, the opening may be increased from the idle rotation opening to an opening for a high-speed rotation.
Two types of throttle lever apparatuses for adjusting of the opening of the throttle valve are generally known. Which is an automatic idle rotation opening restoring type in which when the throttle lever is released from the rotationally operated state, the lever together with the throttle valve is automatically returned to the intact position (idle rotation opening). The other is an idle opening non-restoring type in which when the operator's fingers merely removed from the throttle lever, the throttle lever is not moved but can be constantly maintained at a desired rotationally operated position (see, e.g., Japanese Utility Model Publication No. 57-19944).
In the automatic idle rotation opening restoring type, when the operator's fingers are removed from the throttle lever during operation of the work machine driven by the internal combustion engine, the internal combustion engine automatically returns to the idling state and in the case where the work machine transmits power from the internal combustion engine to a working unit including of a cutter through a centrifugal clutch, the centrifugal clutch is cut off under the idling state to interrupt power transmission to the working unit. Accordingly, in the event that an accident occurs during the operation of the work machine and power transmission to the working unit comprised of the cutter is required to be interrupted, the throttle valve can be returned immediately to the idle rotation opening by only releasing fingers from the throttle lever and driving of the working unit can be stopped. Therefore, from the standpoint of safety during operation, the automatic idle rotation opening restoring type is superior to the idle opening non-restoring type.
In the automatic idle rotation opening restoring type, an, automatic return to the idling state can be ensured by releasing the operator's fingers from the throttle lever. However, a desired rotationally operated position must be maintained by the operator's constantly holding or gripping the throttle lever by fingers.
The throttle cable connecting the throttle valve and the throttle lever is tortuous in many directions on the way to the throttle lever from the throttle valve. Moreover a return spring of the throttle valve is required to have a certain force enough to steadily return the throttle valve. Accordingly, in order to maintain a desired rotationally operated position by holding the throttle lever by the operator's fingers during operation of the work machine, an operation force for opposing the throttle cable and tension of the return spring is needed. Unfortunately when the throttle lever is gripped by the operator's fingers for a long time, the operator's fingers are becomes fatigued.
More particularly, the automatic idle rotation opening restoring type requires fingers to exert strong (highly depressive) holding force on the throttle lever during its normal operation. Thus difficulties with ease of operation arise and in spite of the aformentioned advantage of high safety. This type of apparatus is not appreciated much by the operator and thus, the work machine is hardly equipped with this type of apparatus.